gist/20171221/BellmanFord.cs

using System;
using System.Collections.Generic;
using System.Linq;

// Adapted from JavaScript example in The Imposter's Handbook by Rob Conery

namespace BellmanFord
{
    class Path
    {
        public string From;
        public string To;
        public int Cost;

        public Path(string from, string to, int cost)
        {
            From = from;
            To = to;
            Cost = cost;
        }
    }
    class Program
    {
        static string[] vertices = { "S", "A", "B", "C", "D", "E" };

        static List<Path> graph = new List<Path>()
        {
            new Path("S", "A", 4),
            new Path("S", "E", -5),
            new Path("A", "C", 6),
            new Path("B", "A", 3),
            new Path("C", "B", -2),
            new Path("D", "C", 3),
            new Path("D", "A", 10),
            new Path("E", "D", 8)
        };

        static Dictionary<string, int> memo = new Dictionary<string, int>()
        {
            { "S", 0 },
            { "A", int.MaxValue },
            { "B", int.MaxValue },
            { "C", int.MaxValue },
            { "D", int.MaxValue },
            { "E", int.MaxValue }
        };

        static bool Iterate()
        {
            bool doItAgain = false;

            foreach (var fromVertex in vertices)
            {
                Path[] edges = graph.Where(x => x.From == fromVertex).ToArray();
                foreach (var edge in edges)
                {
                    int potentialCost = memo[edge.From] == int.MaxValue ? int.MaxValue : memo[edge.From] + edge.Cost;
                    if (potentialCost < memo[edge.To])
                    {
                        memo[edge.To] = potentialCost;
                        doItAgain = true;
                    }
                }
            }
            return doItAgain;
        }

        static void Main()
        {
            for (int i = 0; i < vertices.Length; i++)
            {
                if (!Iterate())
                    break;
            }

            foreach (var keyValue in memo)
            {
                Console.WriteLine($"{keyValue.Key}: {keyValue.Value}");
            }
        }
    }
}